The present invention relates to a method for fabricating a thin layer, and, more particularly, to a method for fabricating a ruthenium (Ru) thin layer by using an atomic layer deposition (ALD) technique.
A chemical vapor deposition (CVD) technique has been used to deposit a layer on a substrate such as a silicon wafer. A precursor used in the CVD technique is a thermally decomposed volatile compound to be adsorbed into a heated substrate at a temperature that exceeds the decomposition temperature. Layers, such as a metal, a metal mixture, a metal alloy, a ceramic, a metal compound and a mixture thereof, are deposited by the CVD technique, dependent on selection of and reaction conditions of a precursor.
A ruthenium (Ru) layer formed by the CVD technique in an integrated circuit process of a semiconductor device has an excellent conductivity, a high stability in a wide temperature range and a good adhesion with a silicon layer, a silicon oxide layer and a ceramic oxide layer.
The Ru layer formed by the CVD technique is employed as an electrode of a capacitor or a wire material in giga DRAMs and FRAMs. Because the Ru layer scarcely reacts on a silicon or metal oxide, the Ru layer may be used as a barrier layer against silicon or oxygen. Also, the Ru is used as a catalyst in polymer synthesis processes.
Recently, a Ru precursor has been used in a CVD technique.
A conventional method for fabricating a Ru layer will now be described. Ru precursor compounds of a conventional Ru layer used in the CVD technique are RuX2 or RuX3 (where, X represents an anionic ligand), of which oxidation states are of +2 and +3 respectively, and oxygen (O2) or hydrogen (H2) gas is used as a reaction gas.
At this time, the oxygen reduces the Ru by a reaction with the Ru precursor compound and reacts with the anionic ligand xe2x80x9cXxe2x80x9d to generate by-products. The ligand is any one of atoms, molecule or ions (NH3, H2O, Clxe2x88x92, CNxe2x88x92 or the like), which have non-covalent electron pairs. xe2x80x9cXxe2x80x9d of RuX2 and RuX3 is xcex2-diketonate, cyclopentadienyl or alkylcyclopentadienyl. The Ru precursor compounds (RuX2, RuX3) and by-products is produced by the following reactions:
RuCl3+3HXxe2x86x92RuX3+3HCl, or
RuCl3+2HXxe2x86x92RuX2+2HCl (add a reducing agent such as Zn or the like)
RuX2, RuX3+O2xe2x86x92Ru(C, H, O)+CxHyOz
The last equation represents a CVD reaction of the Ru precursor compounds. In these oxidation and reduction reactions, neutral products, such as an alkene of CO, H2, butene or the like, and anionic and cationic products, such as alkyl and xcex2-diketonate of H, butyl or the like, are produced.
The neutral products may be removed by using a vacuum pump but the anionic and cationic products may be remained in the Ru thin layer as impurities. The reaction of oxygen and the ligand is not only complex, but also rapidly performed so that impurities such carbon, hydrogen and oxygen remain in the Ru thin layer. The remaining impurities are diffused into an external layer from the Ru thin layer during a thermal treatment process for making the dense Ru thin layer or the following processes so that characteristics of the Ru thin layer and peripheral layers are aggravated.
To solve the above problem, in case of using hydrogen, which is a reducing gas, as a reaction gas, because a deposition temperature has to be set at over 600xc2x0 C. in order to activate the hydrogen, the Ru precursor previously undergoes decomposition and then a carbonate or an oxide are produced so that impurities still remain in the Ru layer. When the Ru thin layer is used as an electrode of a capacitor using dielectric layers such as Ta2O5, BST, PZT, SBT and the like, if the H2 gas is used at a high temperature, H2 reduces the dielectric oxide layer so that the desired electrical characteristics cannot be obtained.
When the Ru thin layer is deposited by the CVD technique using the Ru precursors (RuX2 and RuX3), non-volatile materials, such as carbonate, oxide and the like, are also produced by the gas-phase reaction between a reaction gas and the Ru precursor. These non-volatile materials exist in the Ru thin layer and cause generation of particles.
A method for fabricating a ruthenium thin layer by using an atomic layer deposition technique is disclosed.
In accordance with one embodiment, a method for fabricating a Ru thin layer comprises: loading a substrate into a reaction chamber for an atomic layer deposition; adsorbing RuXn (wherein n is 2 or 3), which is a Ru precursor, onto the substrate; and injecting a reductive reaction gas into the reaction chamber.